The present invention relates to a housing structure, in particular to a housing structure which can be favorably employed for a in-vehicle electronic device such as an airbag Electronic Control Unit (ECU).
FIG. 1 is an exploded perspective view illustrating an airbag ECU to which a housing structure for an in-vehicle electronic device according to a first related art is applied. For example, Patent Document 1 discloses the first related art. The airbag ECU is mounted on a vehicle. The airbag ECU controls a gas generator so as to activate the gas generator when detecting a shock to a vehicle body due to a collision to supply the gas from the gas generator to an airbag.
The airbag ECU 1 includes a housing 4 which has a case body 2 and three brackets 3a, 3b, 3c integrally formed in the case body 2 for mounting the case body 2 on the vehicle body. The airbag ECU 1 further includes a control board 6 which is an in-vehicle electronic device on which an acceleration sensor for detecting the shock due to the collision is mounted, a lid 8 which is fixed to the housing 4 with a plurality of bolts 7 when the control board 6 is accommodated in the housing 4, and a connector 10 fitted into a fitting recess 9 formed at one side of the housing 4.
Functions required for the housing 4 are as follows: (1) precisely transmitting the shock due to the collision of the vehicle to the acceleration sensor mounted on the control board 6; and (2) protecting the control board 6 from an external load applied to the housing 4 due to the collision of the vehicle so that the control board 6 can continue to function normally even after the collision.
Regarding the second function (2) of these two functions required for the housing 4, Patent Document 2 discloses a second related art. According to the second related art, the brackets 3a, 3b, 3c is intentionally designed to be broken by the shock transmitted from the vehicle body to the housing 4 to protect the control board 6. In this structure, each of the brackets 3a, 3b, 3c is broken at a position lower than a mounting position of the control board 6 in the housing 4. In other words, each of the bracket 3a, 3b, 3c is broken at its base end side. Accordingly, a metal piece generated when each of the brackets 3a, 3b, 3c is broken does not fall on the control board 6, thereby preventing a circuit of the control board 6 from being broken.
Since the airbag ECU 1 is mounted on any vehicle as a standard equipment, an outer shape of the airbag ECU 1 and a attachment structure to the vehicle body are standardized. In a model change of the airbag ECU 1, the control board or the housing 4 may be required to be reduced in size. However, if the attachment structure of each bracket 3a, 3b, 3c to the vehicle is changed in the model change, it is necessary to also change the standard of the attachment structure or change the structure of the vehicle body. Accordingly, even in such a model change, the attachment structure of the housing 4 to the vehicle body is not changed and only an attachment portion of the control board 6 to the housing 4 may be reduced in size.
FIG. 2 is a top plan view for explaining a change of the structure of an airbag ECU 10 according to a third related art due to the downsizing. FIG. 3 is a perspective view for explaining the change of the structure of the airbag 10 shown in FIG. 2. In FIG. 2, the airbag ECU 1 according to the first and second related arts is represented in solid lines and the airbag ECU 10 according to the third related art is represented in dashed lines.
In accordance with a requirement for further cost reduction of the airbag ECU 1, a control board 11 of the airbag ECU 10 according to the third related art is reduced in size relative to the control board 6 according to the first and second related arts. In a housing 15 of the airbag ECU 10, fixing positions 12a, 12b, 12c to be fixed to the vehicle body with fixing means such as bolts and the case body 13 which is reduced in size in accordance with the downsized control board 11 are connected by long brackets 14a, 14b, 14c. Accordingly, gap between each fixing position 12a, 12b, 12c and the case housing 13 becomes large.
In such an airbag ECU 10 according to the third related art, since each bracket 14a, 14b, 14c is relatively long, transmissibility of the shock is reduced. In order to solve such a problem, a fourth related art discloses an airbag ECU 16 which employs a housing 18 in which flange portions 17a, 17b continuously and integrally formed between the brackets 14a, 14b, 14c in a single surface, as shown in a perspective view of FIG. 4.
Further, as shown in a perspective view of FIG. 5, a fifth related art discloses, as another reinforcement configuration, an airbag ECU 22 which employs a housing 21 in which ribs 20a, 20b, 20c are integrally formed between each of the brackets 14a, 14b, 14c and the case body 13.
Patent Document 1: Japanese Patent Publication No. 2006-306307A
Patent Document 2: Japanese Patent Publication No. 2002-308021A
In the above describe fourth related art, since the flange portions 17a, 17b are integrally formed between each bracket 14a, 14b, 14c in the housing 18, the weight of the airbag ECU 19 increases, and thus the manufacturing cost also increases.
In the fifth related art, each rib 20a, 20b, 20c are integrally formed between each bracket 14a, 14b, 14c and the case body 13 in the housing 21. When the airbag ECU 22 is mounted on a vehicle and the shock is applied to the housing 21 due to the collision of the vehicle, the impact force is transmitted to the case body 13 through each bracket 14a, 14b, 14c and each rib 20a, 20b, 20c, and thus the case body 13 may be broken at a position upper than higher than the control board 6, i.e. a position at a side of a top plate 23. Therefore, as well as the first related art, the fifth related art has a problem that scattered articles such as a metal piece, generated due to the breakage of the case body 13 may fall on the control board 6 and the circuit of the control board 6 may be broken. In addition, since each bracket 14a, 14b, 14c are reinforced by each rib 2a, 20b, 20c, the brackets 14a, 14b, 14c have high rigidity. Therefore, the shock transmission performance from each bracket 14a, 14b, 14c to the case body 13 may be reduced.